No errors in 'luaO_pushvfstring'

Any call to 'va_start' must have a corresponding call to 'va_end';
so, functions called between them (luaO_pushvfstring in particular)
cannot raise errors.

lauxlib.c

@@ -225,7 +225,7 @@ LUALIB_API void luaL_where (lua_State *L, int level) {
 /*
 ** Again, the use of 'lua_pushvfstring' ensures this function does
 ** not need reserved stack space when called. (At worst, it generates
-** an error with "stack overflow" instead of the given message.)
+** a memory error instead of the given message.)
 */
 LUALIB_API int luaL_error (lua_State *L, const char *fmt, ...) {
   va_list argp;